Unit 3, Lesson 3
Representing Proportional Relationships
Grade 8
Preparation
Lesson Narrative
In this lesson students label and choose a scale for empty pairs of axes in order to graph a proportional relationship. First, students create a graphical representation of a proportional relationship when given a table and a description to start from. They learn that the rate of change in a proportional relationship is the same as the constant of proportionality: the amount one variable changes by when the other variable increases by 1. Next, students use the Info Gap structure to graph a proportional relationship on an empty pair of axes that includes a specific point. Students will need to request information about the proportional relationship as well as calculate the specific point. The focus is on the graphs students create and their decisions on how to scale the axes in an appropriate manner for the situation (MP4).
- Create an equation and a graph to represent proportional relationships, including an appropriate scale and axes.
- Determine what information is needed to create graphs that represent proportional relationships. Ask questions to elicit that information.
Let's graph proportional relationships.
Required Preparation
None
The rate of change is the amount changes when increases by 1. On a graph, the rate of change is the slope of the line.
In this graph, increases by 15 dollars when increases by 1 hour. The rate of change is 15 dollars per hour.
Graph, horizontal axis, x, amount earned in hours. vertical axis, y, amount earned in dollars. line starting at 0 comma 10, passing through 2 comma 40 and 60 comma 100.